This invention relates to a controller for a direct current motor which drives an aircraft passenger boarding bridge. More specifically, it relates to a controller for a three-phase powered, variable speed, reversible, direct current motor which drives an aircraft passenger boarding bridge. This motor may be series-wound, shunt-wound, compound-wound, permanent magnet, etc.;
In order to service an aircraft, the end of an aircraft passenger boarding bridge remote from the terminal must be driven toward and away from a parked aircraft. Typically, a set of wheels which support the remote end of the bridge are driven by an electric motor to move the bridge. Because of the relatively heavy weight and massive structure of a bridge, precise control of the drive motor is required to assure that the bridge does not contact an aircraft with sufficient force to cause damage to it. Such a motor must be reversible and must be able to drive the wheels at various speeds so that the speed of the bridge can be reduced as it approaches an aircraft. The direct current motor controller of the instant invention sets the speed and direction of rotation of the d.c. motor which drives the wheels mounted on the bridge.
The speed of a d.c. motor is a function of the field and armature voltages. Control and adjustment of armature voltage results in a variable speed constant torque drive. Control and adjustment of field voltage results in a constant horsepower drive. For aircraft passenger boarding bridge application, it is desirable to provide a variable speed constant torque drive. Accordingly, the controller of the instant invention adjusts the speed of the motor by regulating armature voltage. Direction of rotation of a d.c. motor is determined by whether power is supplied to the motor from the positive or negative half of the three-phase alternating current power input. During operation of the motor, one set of switching devices is actuated sequentially by the controller to cause a portion of the positive half of the line phases to pass to the motor armature to cause the motor to rotate in one direction or another set of switching devices is actuated sequentially to cause a portion of the negative half of the line phases to pass to the armature to cause the motor to operate in the other direction.
Motor speed is controlled by modulating the percentage of the total time period of each of the three phases during which the phases are connected to the armature, from a minimum of 0 to a maximum of 100 percent. In some d.c. motor controllers presently in use, a ramp in the form of a linearly increasing or decreasing voltage is generated and timed such that the initial voltage of the ramp begins to decrease or increase at the beginning of the maximum time period of a line phase in a three-phase system and the end of the ramp is timed to coincide with the end of the period of the line phase. In order to determine the period of time each phase is connected to the motor armature in order to have the motor attain a commanded speed, a reference voltage corresponding to the commanded speed is compared with the ramp voltage. The controller is adjusted such that for maximum speed the reference voltage equals the ramp voltage correponding to the beginning of the period of one phase and for 0 speed the reference voltage equals the ramp voltage corresponding to the end of the period of one phase. When the ramp voltage falls or rises to the reference voltage, the controller supplies a signal which actuates appropriate switching devices which sequentially connect the positive or negative portions of the line phases to the motor armature for the length of time required for the motor to attain the commanded speed and direction of rotation.
Because of the relatively large mass of an aircraft passenger boarding bridge a controller for a motor driving the bridge must be able to safeguard the motor and the bridge when a commanded input to the motor exceeds the capability of the motor or the drive mechanism. For example, the controller must set a rate of response of the motor to a commanded input which will not allow the motor to spin the wheels of the bridge drive when the input is calling for the drive to accelerate the bridge. Additionally, the motor controller must be able to prevent the commanded input from commanding a speed which will cause the motor to require a current or voltage in excess of its rated maximum. Further, the controller must insure that the bridge has stopped moving in one direction before it actuates the switching devices which pass line phases of opposite polarity to drive the motor in the other direction. Also, when the commanded input is less than the speed of the bridge and the bridge is driving the motor the controller should be able to cause the motor to go into a regeneration mode and give up power to the line so that the motor will help decelerate the bridge.
A controller for a motor which drives an aircraft passenger boarding bridge must be able to interrupt power to the motor under a number of conditions for safety reasons. Some of these conditions are when a bridge "run" switch on the operator control console is open, when a "disable" switch at a remote location such as at the motor when the drive is being serviced is open, when one of the three line phases is missing or the phases are out of order and when the motor is overloaded.
In known three-phase, half wave powered, variable speed, reversible d.c. motor controllers, six ramp generators are required; one for the positive and one for the negative half of each of the three line phases. Each ramp generator has a potentiometer, a current limiter, a voltage divider, a ratio compartor, etc. Additionally, since the ramps for the three phases must be generated sequentially, the ramp generators must be adjusted to precisely follow each other. These adjustments are critical, difficult to attain and difficult to maintain. Thus, such controllers have many components, are large, complex, expensive, and require numerous critical adjustments. It is desirable to provide a controller for a three-phase, half wave powered, variable speed, reversible, direct current motor which is relatively simple, inexpensive, compact and does not require multiple ramp generators and numerous adjustments in order to sequentially generate a ramp for each of the three phases. It is also desirable to provide a controller for a direct current motor which drives an aircraft passenger boarding bridge, which provides an adjustable motor response rate which limits the input command to prevent the motor from requiring a current or voltage in excess of its rated maximum, which prevents simultaneous connection of line phases of opposite polarity and which enables the motor to regenerate power to the line.
Additionally, it is desirable to provide a controller for a direct current motor which drives an aircraft passenger boarding bridge which interrupts power to the motor when line power phases are missing or out of order, when control switches are open and when the motor is overloaded.